1. Field of the Invention
The present invention relates to a ferrule transfer method of transferring a ferrule with a built-in optical fiber that is fusion-spliced with an optical fiber to a fusion-spliced-portion reinforcing device and a ferrule holder for holding the ferrule.
2. Description of the Related Art
Recently, with the prevalence of FTTH (Fiber To The Home) and the like, an optical communication network is widely used at general households. Along with this condition, various splicing methods of assembling an optical connector without performing a polishing step and splicing optical fibers are employed at a splicing site.
As the optical connector, there is known a mechanical optical connector in which one end of a built-in optical fiber matches a splicing end of the ferrule and the other end of the built-in optical fiber is protruded from the other end of the ferrule where a mechanical holding unit is provided (see, for example, Japanese Patent Application Laid-open No. H10-206688, Japanese Patent Application Laid-open No. H11-142686, Japanese Patent Application Laid-open No. H11-142687, Japanese Patent Application Laid-open No. H11-160563, and Japanese Patent Application Laid-open No. 2000-347068). In the mechanical optical connector, the other end of the built-in optical fiber and one end of another optical fiber are mechanically held to splice them in such a manner that their axis centers match each other so that an optical connector can be provided on the one end of another optical fiber.
In these days, an optical connector is provided in which a built-in optical fiber and another optical fiber are fusion-spliced to enhance a long-time reliability (see, for example, Japanese Patent Application Laid-open No. 2002-82257).
FIG. 19 is a schematic partial section view of a conventional optical connector 10 disclosed in Japanese Patent Application Laid-open No. 2002-82257. The optical connector 10 includes a ferrule 11, a built-in optical fiber 12, a housing 15, and a coil spring 20, and is fusion-spliced with an optical fiber core 14, with a fusion-spliced portion reinforced with a reinforcing body 13.
The housing 15 includes a plug housing 16, a stopper ring 17, and a boot 18. The plug housing 16 and the stopper ring 17 are coupled by engaging an engagement hole 16a and an engagement protrusion 17a. The boot 18 is attached to the stopper ring 17 that constitutes a rear portion of the housing 15. The boot 18 includes an attaching portion 18a and a bending portion 18b. The coil spring 20 is placed between the ferrule 11 and the stopper ring 17, holding the ferrule 11 in a movable manner in an axis direction.
The built-in optical fiber 12 is formed by cutting in advance an appropriate optical fiber by a predetermined length at a manufacturing factory, and inserting and fixing it in the ferrule 11. One end of the built-in optical fiber 12 and a splicing end of the ferrule 11 are polishing-processed in advance, and are processed not to cause splicing loss with another optical connector spliced. On the other hand, removal of a coating and end processing for fusion splicing are required for the other end of the built-in optical fiber 12 that protrudes backward of the ferrule 11, which are generally performed in advance at a manufacturing factory and the like.
Removal of a coating and end processing with regard to the optical fiber core 14 to be spliced to the optical connector 10 are performed at the splicing site. Machine tools for the processing are provided at the splicing site.
FIGS. 20 to 22 depict an operation of fusion splicing between the built-in optical fiber attached by insertion into the ferrule 11 and the optical fiber core 14. The operation of fusion splicing is performed at the splicing site. Prior to the fusion splicing, as shown in FIG. 20, at the end of the built-in optical fiber 12 that is to be fusion-spliced, a coating 12a is removed so that a bare optical fiber portion 12b is exposed in advance at a factory as described above. In addition, at an end of the optical fiber core 14, a coating 14a is removed so that a bare optical fiber portion 14b is exposed. Then, the bare optical fiber portions 12b and 14b are placed at a fusion-splicing device by a holder that holds them, their centers are aligned on a V-shaped groove of the holder, and the bare optical fiber portions 12b and 14b are clamped. Then, as shown in FIG. 21, an electric discharge is applied to them through an arc discharge A from discharge electrodes 22a to heat them for fusion splicing, thereby forming a fusion-spliced portion 19. Mechanical strength of the fusion-spliced portion 19 is degraded because of removed coating so that the fusion-spliced portion 19 is transferred to a later-described fusion-spliced-portion reinforcing device. Then, as shown in FIG. 22, the fusion-spliced portion 19 is covered by the reinforcing body 13.
The reinforcing body 13 is a heat-shrinkable tube that includes a reinforcing member such as metal and thermoplastic resin. The fusion-spliced portion 19 is covered by the reinforcing body 13 and is transferred to the fusion-spliced-portion reinforcing device. The reinforcing body 13 is heated and contracted so that it covers the fusion-spliced portion 19. Besides using the reinforcing body 13 as a means of protecting the fusion-spliced portion, a recoating method of coating the fusion-spliced portion with a UV-curing resin and hardening the UV-curing resin to form a coating layer is also used.
FIG. 23 is a view of an example of a main unit of a conventional fusion-splicing device 21 that fusion-splices optical fibers. It is indicated that a fusion-splicing operation unit 22 is arranged at the center and a fusion-spliced-portion reinforcing device 23 is arranged above the fusion-splicing operation unit 22. Optical fiber holders H that causes optical fibers F to face each other on their ends to arrange and fix them are arranged both sides of the fusion-splicing operation unit 22, and the discharge electrodes 22a to cause the arc discharge are arranged at its center. The fusion-spliced-portion reinforcing device 23 includes a long heating chamber 23a that extends laterally in a straight line and holders 23b that are arranged at both ends of the heating chamber 23a and that give tension to fusion-spliced optical fibers and hold optical fibers F. A reference sign 22b is a lid that covers the fusion-splicing operation unit 22 and a reference sign 23c is a lid that covers the fusion-spliced-portion reinforcing device 23.
When the built-in optical fiber 12 fitted into the ferrule 11 and the optical fiber core 14 are fusion-spliced by the fusion-splicing device 21, one of optical fiber holders is replaced with a ferrule holder.
To attach a reinforcing body to the fusion-spliced portion of the ferrule in which the optical fiber and the built-in optical fiber are fusion-spliced and to give a mechanical protection as described above, it is necessary to transfer the ferrule from the fusion-splicing operation unit of the fusion-splicing device to the fusion-spliced-portion reinforcing device. However, because an optical fiber is not attached at the splicing end of the ferrule, it is impossible to hold and transfer each of optical fibers as in a case of a conventional fusion-splicing of optical fibers. For this reason, as shown in FIG. 24, it is considered that the ferrule 11 and the optical fiber core 14 are pinched by a pinching device 25 that includes pinching units 25a, 25a having a shape like a clothespin and are transferred from the fusion-splicing operation unit 22 to the heating chamber 23a of the fusion-spliced-portion reinforcing device 23. The pinching device 25 in which the pinching units 25a, 25a are coupled by a rod-shaped coupling member 25b having a predetermined length to maintain a predetermined distance therebetween is arranged and is constituted not to give a tension to the fusion-spliced portion when transferring the ferrule and the optical fiber.
However, to accommodate the fusion-spliced portion 19 and the reinforcing body 13 in the heating chamber 23a using the method of pinching the ferrule 11 and the like by the pinching device 25 and transferring them, because the heating chamber 23a has a narrow insertion slot, the pinching device 25 should be reduced in size to be accommodated in the heating chamber 23a while the pinching device 25 pinches the ferrule 11 and the like, or the reinforcing body 13 and the ferrule 11 have to be fallen in the heating chamber 23a by stopping pinching the ferrule 11 above the heating chamber 23a. However, when accommodating the ferrule 11 by use of the small pinching device 25 in the heating chamber 23a, it is impossible to close the lid 23c of the fusion-spliced-portion reinforcing device 23. This makes it impossible to stably contract the reinforcing body 13 like a heat-shrinkable tube. Alternatively, a method can be considered that an equivalent for a lid is arranged around the pinching device 25 and the equivalent covers the heating chamber 23a. However, the method causes problems of a poor workability, a higher price because of a higher component count, and the like. Furthermore, the method of falling the reinforcing body 13 and the ferrule 11 from above the fusion-spliced-portion reinforcing device 23 has problems of a possibility of cutting the fusion-spliced portion 19 due to an impulse of falling, being unable to contract the heat-shrinkable tube in a good shape because fusion-spliced optical fibers cannot be straightly held, and the like.